Is there a risk in new clazz(this) from Clazz.clone?

Question

After a build break, one developer complained it was because the previously available Clazz.clone() (not the real name of the class :)) has been removed, so his call to clz.clone() is breaking.

Upon which the author of Clazz advised that the client code be changed to use new Clazz(clz). \

Is there risk in implementing the clone method to return new Clazz(this)? What could go wrong?

B-Rad · Answer 1 · 2014-07-25T14:10:19.107

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I don't believe there is risk in doing that, but it's unnecessary. Have your one developer change his function call.

// this is the same
var myClazz = thatClazz.clone();

// as this
var myClazz = new Clazz(thatClazz);

The new method uses something called a Copy Constructor which in my opinion looks cleaner than using .clone().

Further, a discussion should be had with your development team about modifying code that other modules are dependent on. Any methods or properties that are not private should have references checked before a change.

edited Jul 25 '14 at 14:10

answered Jul 25 '14 at 13:59

B-Rad

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@DmitryGinzburg it is Java if `Clazz` is subtype of `var`, no? – Miserable Variable Jul 25 '14 at 14:24
This is true, but I think it still tackles elements of the problem. – B-Rad Jul 25 '14 at 14:25
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the benefit of clone() is that it is polymorphic, copy constructor is not! – sodik Jul 25 '14 at 14:26

laune · Answer 2 · 2014-07-25T15:01:06.413

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The major difference is that clone is a method and a constructor is a constructor.

This means that

Clazz x = ...; 
Object xClone = x.clone()

returns whatever method clone of x.getClass() returns: a Clazz object or an object of a subclass of Clazz. Compare this to

Clazz x = ...;
Object xCopy = new Clazz( x );

which will give you a Clazz object, even when x references a SubClazz extends Clazz.

Presumably this doesn't matter to "the author of Clazz".

edited Jul 25 '14 at 15:01

answered Jul 25 '14 at 14:21

laune

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There are many instances when `new Clazz(x)` should /not/ return a subclass but rather fail loudly. Slicing is not always good. – Miserable Variable Jul 25 '14 at 15:11
Now I see that you did not. Since I was asking specifically for risks in using clone I perhaps misinterpreted your description of difference between a method call and a constructor call to imply some benefit/loss analysis – Miserable Variable Jul 25 '14 at 15:38

score 2 · Answer 3 · edited May 23 '17 at 10:25

There's lots of discussion around clone vs copy constructor on the internet, eg Clone() vs Copy constructor- which is recommended in java

Adding a clone method will work but given that this is all internal code, why introduce the extra complexity?

It does sound like you could do with a process to handle breaking changes. May be just do something simple such as mark clone as deprecated for a while to give developers a chance to stop using it.

I've seen people waste hours trying to maintain backward compatibility on internal apis and more hours arguing about trivial changes like this.

Is there a risk in new clazz(this) from Clazz.clone?

3 Answers3